Rotary cutters are used in the printing industry to sever and perforate, as the case may be, moving web materials such as paper. Incisions are generally made transverse to the direction of web travel, and serve to separate the web into discrete predetermined lengths or create tear lines at predetermined locations along the length of the web. A rotary cutter typically comprises a pair of synchronized counter-rotating knife and anvil cylinders between which the web passes. The knife cylinder is equipped with one or more knife blades (or knives) that generally extend parallel to the rotational axis of the knife cylinder, and cut or perforate the web against the anvil cylinder. In known web-type printing press operations that produce a printed product from a moving paper web, the printed product may pass through other auxiliary equipment performing additional operations before being forwarded to the rotary cutter. A single knife blade can be mounted to the knife cylinder to produce what has been termed a butt cut in web material. Mounting a pair of knife blades circumferentially adjacent each other produces what has been termed a bleed cut, resulting in a trim piece or chip being formed that must be discarded.
Because the circumference of a knife cylinder is fixed, the lengths of the segments into which a web can be cut are varied by changing the circumferential locations of multiple knife blades mounted to the knife cylinder, resulting in multiple cuts being produced in the web with each revolution of the knife cylinder. Rotary cutters designed to be reconfigurable for processing various different products are referred to as variable product rotary cutters, or simply variable rotary cutters. Virtually all variable rotary cutters utilize knife holders (or knife blocks) that house the knife blades. “Make-ready” is a term of art that is understood to mean the process of setting up a rotary cutter by mounting knife holders to a knife cylinder before running a job.
One configuration of a variable rotary cutter employs knife holders mounted to the knife cylinder by a dovetail lock-up design in the surface of the cylinder face. In another configuration, multiple tapped holes are formed in the surface of the cylinder face to clamp knife holders onto the cylinder. Knife holder sizes are matched to the lengths of the knife blade with which they are to be used, and knife blades are mounted in their respective holders off the cutting machine. During make-ready, the operator must know the format of the finished product including the final product length, the number of product streams that will simultaneously pass through the rotary cutter, and the width of each stream. In addition, it is important to know where these streams will be relative to the centerline (axial midpoint) of the cylinder, i.e., left or right of the centerline. Two product streams side-by-side with widths of less than 12 inches (about 30 cm) are most common, in which case two 12-inch holders, each carrying a 12-inch knife blade, would be used.
Once the above information is retrieved, the knife holders are mounted in the strategic locations both circumferentially and axially on the cylinder surface to produce the desired products. Proper positioning of the knife holders requires a locating device and indexing of the cylinder. The knife cylinder is rotated until a location at which a knife blade is required is accessible to the operator. A knife holder (with a mounted knife blade) is placed on the cylinder and its location precisely determined with the locating device. The holder is then secured to the cylinder, after which the cylinder is again indexed to the next location requiring a knife blade. This process is repeated for each knife holder, resulting in a very tedious and time-consuming process.
When the particular job is finished and a new job with a different product format is to be run, all of the knife holders are removed from the cylinder and the entire process is repeated. On occasion, the product lengths might be the same from job to job, however the product stream width and/or location (left or right) often differ, requiring the holders to be removed and remounted left or right to line up with the printed streams.
In other rotary cutters, the knife cylinder has a plurality of knife holders circumferentially positioned about the circumference of the knife cylinder. At least some of the knife holders extend the axial length of the knife cylinder and are configured to permit multiple knife blades of different lengths to be mounted therein end-to-end across the entire axial length of the knife cylinder. At least one knife blade can be mounted in at least a first of the knife holders, while knife blades are not mounted in at least a second of the knife holders so that rotation of the knife cylinder against a web material forms incisions spaced apart a first spacing distance in the web material. Thereafter, the knife cylinder can be reconfigured without repositioning any of the knife holders on the knife cylinder, but instead by removing, repositioning, and/or installing knife blades on the knife holders. An example of such a device can be found in U.S. Patent Application Publication No. 2005/0247174 to Scheffer, et al., which is incorporated by reference herein in its entirety.
As discussed above, typical rotary cutters include two cylinders that rotate relative to each other. Knife blades are mounted to one cylinder and the other cylinder acts as an anvil that provides a surface against which to sandwich the web material between the knife blade to perform the cut.